1. Field of The Invention
This invention relates to metal cleaning compositions for metals and more particularly, to metal cleaning compositions for steel plates which are used in the final stand of a tandem mill in order to ensure washing of steel plates without corroding the metal being contacted therewith.
2. Description of The Invention
Metals suffer corrosion when contacted with water. Especially, corrosion becomes considerable when water contacting with metals is acidic in nature or contains dissociated ions such as of sodium chloride, thus steel plate manufacturer incurring a great loss. In case where an alkaline washing solution is used in the washing step of metal, corrosion involved is not so excessive. However, when a neutral washing solution is used, a diversity of dissociated ions contained in the solution will cause a problem of corrosion of a variety of metals constituting the apparatus such as iron, steel, copper, brass and the like.
A number of attempts were made in order to avoid the corrosion. For instance, there were developed and widely used rust or corrosion preventives for copper such as benzotriazole, methylbenzotriazole, ethylbenzotriazole, benzothiazole, 2-mercaptobenzothiazole and the like. Alternatively, hydroxyquinoline and salts thereof were developed as an inhibitor for use in the acid cleaning step of a copper plate-making process. However, these corrosion or rust preventives do not show any satisfactory corrosion preventive effects when used singly or in combination as a cleaning agent for readily corrosive metals. This is because the known rust preventives are usually deposited on the metal surface in the form of a film but the film has inevitably defects therein, so that anodes are locally formed and thus corrosion is accelerated on the contrary. In some case, pitting corrosion may take place. Moreover, when applied as metal cleaning agents, rust preventives not only should develop the rust preventing effect, but also should not lower the cleaning effect, not cause oil stain and oil-burnt stain, and not adversely affect the annealing step without involving environmental pollution.